The invention described herein may be manufactured, used and licensed by or for the U.S. Government.
1. Field of the Invention
The invention relates to decontamination of chemical warfare agents. More particularly, the invention relates to the decontamination of mustard agents such as HD by oxidation, as well as nerve agents such as VX and GD by perhydrolysis, using environmentally safe reactants.
2. Description of the Related Art
Several types of toxic chemical compounds are known to be useful as chemical warfare agents. These include mustard agents or gases known as blister agents, such as bis-(2-chloroethyl)sulfide, also known as HD, and nerve agents such as pinacolyl methylphosphonofluoridate, which is also known as GD, and O-ethyl S-(2-diisopropylamino)ethyl methylphosphonothioate, which is known as VX. HD is a colorless, oily liquid that is highly insoluble in water, and is a powerful vesicant which primarily affects the eyes and the lungs, blisters the skin and is considered a carcinogen. HD is also cytotoxic to hematopoietic tissue and can be lethal at high doses. GD and VX are powerful nerve agents that attack the nerve cells and impair the functioning of the central nervous system.
In order to decontaminate the vesicant mustard gas to render it non-toxic, it is necessary to oxidize it to the corresponding sulfoxide. Nerve agents such as VX and GD are rendered non-toxic by perhydrolysis to their non-toxic phosphonic acids. For example, the oxidation of HD to HD-sulfoxide (HDO) renders the gas non-toxic. One effective way to conduct this oxidation reaction is by reacting the agent with peroxide compounds. Mildly-basic peroxide is also known to effect the perhydrolysis of VX and GD to their non-toxic phosphonic acids. Peroxides are desirable reactants for decontamination because they are non-toxic and non-corrosive, as compared to hypochlorite-based processes which are toxic and environmentally harmful. Additionally, peroxides are preferable because of their extremely low freezing points. However, while it is desirable to decontaminate chemical warfare agents by oxidation in a peroxide system, presently known systems are inefficient decontaminates because they cause secondary oxidation of the corresponding sulfoxide to a sulfone, a toxic vesicant. For example, HD-sulfoxide is a non-vesicant, while HD-sulfone is a highly toxic vesicant material. Also, known peroxide systems using hydrogen carbonate ions as an activator are inefficient because the oxidation reaction is very slow. However, hydrogen carbonate activator is efficient at generating peroxy anion (OOH31 ) for VX and GD perhydrolysis.
Currently, efforts are being undertaken to speed up the oxidation reaction of HD to its sulfoxide, while avoiding the formation of HD sulfone. The rapid, simultaneous perhydrolysis of VX and GD is also desired. Applicants now have discovered a decontamination system that utilizes a peroxide/molybdate reactant system in a water-in-oil microemulsion. The molybdate in the system acts as a peroxide activator by either generating singlet oxygen (1O2) which diffuses out of the microemulsion and reacts with substrates in a bulk organic solvent, or via generation of peroxomolybdate species of the formula Mo(O)x(Oxe2x80x94O)4xe2x88x92x2xe2x88x92, wherein x=0-3. Applicants have further found that when the peroxomolybdate species is present particularly as a tetraperoxomolybdate Mo(OO)42xe2x88x92dominant species, the decomposition of the peroxide is avoided and 1O2 production is greatly diminished. It has also been found that a tetraperoxo dominant species causes a rapid oxidation of HD to HD-sulfoxide with a rate increase of at least one order of magnitude compared to hydrogen carbonate ion activated systems, while any secondary oxidation of HD-sulfoxide to HD-sulfone occurs at a rate of at least two orders of magnitude slower than a hydrogen carbonate ion activated system. The mild basicity of the molybdate activator further provides for the perhydrolysis of nerve agents VX and GD. The system functions in a variety of microemulsions, exhibits high stability and does not freeze at low temperatures.
The invention provides a process for decontaminating a chemical warfare agent comprising:
contacting at least one compound having a formula selected from the group consisting of
ROP(O)(CH3)F, wherein R is either 2-propyl, pinacolyl, or cyclohexyl;
Rxe2x80x3OP(O)(CH3)SRxe2x80x2, wherein Rxe2x80x3 is ethyl and Rxe2x80x2 is 2-(diisopropylamino)ethyl; and bis(2-chloroethyl)sulfide, with a peroxomolybdate compound having the formula Mo(O)x(Oxe2x80x94O)(4xe2x88x92x)2xe2x88x92, wherein x=0-3
The invention also provides a process for decontaminating a chemical warfare agent comprising:
a) forming a peroxomolybdate compound having the formula Mo(O)x(Oxe2x80x94O)(4xe2x88x92x)2xe2x88x92, wherein
x=0-3 by reacting a peroxide component and a molybdate component; and
b) contacting said peroxomolybdate compound with at last one chemical warfare agent having a formula selected from the group consisting of:
ROP(O)(CH3)F, wherein R is either 2-propyl, pinacolyl, or cyclohexyl;
Rxe2x80x3OP(O)(CH3)SRxe2x80x2, wherein Rxe2x80x3 is ethyl and Rxe2x80x2 is 2-(diisopropylamino)ethyl; and bis(2-chloroethyl)sulfide.
The invention pertains to a process for decontaminating vesicant compounds and nerve agents used as chemical warfare agents. The chemical warfare agents are decontaminated by contacting the agent with a sufficient amount of a peroxomolybdate compound for a sufficient time and under conditions sufficient to produce a non-toxic reaction product. While the present invention is particularly useful for decontamination of mustard gases, it has a broad-spectrum of reactivity toward a variety of chemical warfare agents, even in cold weather operations, while achieving a significant reduction in the toxic, corrosive and environmentally harmful nature of other known decontaminants. The invention is particularly useful for decontaminating vesicant mustard gases. The invention is also useful for decontaminating G and V nerve agents having the following generic formulas: G: ROP(O)(CH3)F, wherein R is either 2-propyl (GB), pinacolyl (GD), or cyclohexyl (GF); V: Rxe2x80x3OP(O)(CH3)SRxe2x80x2, wherein Rxe2x80x3 is ethyl and Rxe2x80x2 is 2-(diisopropylamino)ethyl (VX). More particularly, the chemical warfare agents decontaminated herein include mustard agent bis(2-chloroethyl)sulfide (HD), and nerve agents pinacolyl methylphosphonofluoridate (GD) and O-ethyl S-[2-(diisopropylamino)ethyl]methylphosphonothioate (VX).
The process includes forming a peroxomolybdate compound having the formula Mo (O)x(Oxe2x80x94O)(4xe2x88x92x)2xe2x88x92, wherein x=0-3, in a suitable medium by reacting a peroxide component and a molybdate component in the medium. The preferred medium is a microemulsion which is described below. The peroxide component comprises a material selected from the group consisting of hydrogen peroxide, solid urea hydrogen peroxide, sodium percarbonate peroxide and combinations and derivatives thereof. Of these, the preferred peroxide is a 50% aqueous H2O2. Solid urea hydrogen peroxide is also particularly applicable to address concerns of storage and handling of concentrated aqueous hydrogen peroxide in the field. Additionally, solid urea hydrogen peroxide is non-toxic and environmentally friendly. The peroxide component is preferably present in the microemulsion at from about 1 to about 25 weight percent, more preferably from about 5 to about 20 weight percent, and most preferably from about 8 to about 15 weight percent.
The molybdate component of the invention is comprised of an alkali metal molybdate. The alkali metal preferably comprises a metal selected from the group consisting of Li, Na, K, Rb, Cs, Fr. More preferably, the alkali metal comprises either lithium (Li), sodium (Na) or potassium (K). Most preferably the molybdate component comprises a molybdate potassium salt, particularly K2MoO4. The molybdate component is preferably present in the microemulsion at a concentration of from about 0.001 M to about 1.0 M, more preferably from about 0.01 M to about 0.5 M, and most preferably from about 0.1 M to about 0.2 M.
The reaction of the molybdate component and the peroxide component may be further activated with a carbonate and/or bicarbonate activator. These latter activators work to enhance the perhydrolysis of nerve agents VX and GD to their corresponding phosphonic acids. The carbonate and/or bicarbonate activator is preferably selected from the group consisting of sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, lithium bicarbonate, lithium carbonate, ammonium bicarbonate, ammonium carbonate, hydrogen carbonate, hydrogen bicarbonate, ammonium hydrogen carbonate and combinations thereof. More preferably, the carbonate and/or bicarbonate activator comprises potassium bicarbonate or potassium carbonate. The carbonate and/or bicarbonate activator preferably is present in the microemulsion in an amount of from about 0.01 M to about 2.0 M, more preferably from about 0.1 M to about 1.0 M, and most preferably from about 0.2 M to about 0.8 M.
The reaction of the peroxide component and the molybdate component forms peroxomolybdate compounds in the microemulsion which have the formula Mo(O)x(Oxe2x80x94O)(4xe2x88x92x)2xe2x88x92, wherein x=0-3.The result is a microemulsion that may have four distinct peroxomolybdate species therein, which species comprise monoperoxomolybdate, Mo(O)3(Oxe2x80x94O)2xe2x88x92, diperoxomolybdate, Mo(O)2(Oxe2x80x94O)22xe2x88x92, triperoxomolybdate, Mo(O)(Oxe2x80x94O)32xe2x88x92, and tetraperoxomolybdate, Mo(Oxe2x80x94O)42xe2x88x92. Of these, it has been found that the oxidation of the vesicants to their corresponding non-vesicant sulfoxides is most effective when the dominant peroxomolybdate species comprises the tetraperoxomolybdate species, which is the most active and most stable species. In order for this species to dominate, there must be a high concentration of peroxide in the microemulsion. In the preferred embodiment of the invention, the ratio of hydrogen peroxide to molybdate preferably ranges from about 3.0 to about 3.5,more preferably from about 3.5 to about 4.0,and most preferably the ratio is greater than about 4.0.The preferred result is a microemulsion including less than 10% of each the monoperoxomolybdate, diperoxomolybdate and triperoxomolybdate species, and from about 90% to about 100% of the tetraperoxomolybdate species.
In use, the peroxomolybdate compound may be applied in the form of a spray, a vapor, a liquid, a solid, and/or other physical forms of mixtures that incorporate the peroxide and molybdate components of the decontaminant. Preferably the peroxomolybdate compound is present as a liquid or as a spray. For the peroxomolybdate compound to be applied in a liquid form, it is necessary to disperse the compound in a suitable medium. In one preferred embodiment of the invention, the peroxomolybdate compound is dispersed in a water-oil microemulsion. In this embodiment, the oil preferably comprises either hexane or methylene chloride. Of these, hexane is preferred.
In general, a microemulsion is a transparent or translucent, thermodynamically stable, isotropic dispersion of two immiscible liquids with microdomains of one or both liquids stabilized by an interfacial film of surface-active molecules. It typically comprises water, at least one organic solvent (oil), at least one surfactant, and in most cases at least one co-solvent. The water-in-oil microemulsions are roughly spherical water microdroplets coated by an interfacial film of a surfactant, e.g. sodium dodecyl sulfate (SDS), and a co-solvent, e.g. butanol (BuOH), and dispersed in a continuous phase of oil, e.g. hexane. Other suitable surfactants non-exclusively include cetyl trimethylammonium chloride (CTAC), and polyoxyethylene ethers, such as polyoxyethylene(10) isooctylphenyl ether (Triton X-100). Of these, polyoxyethylene ethers are preferred. Other suitable co-solvents non-exclusively include 2-propanol, 2-methyl-1-propanol and propylene carbonate. Of these propylene carbonate is preferred. The microemulsion may also further include at least one carbonate and/or bicarbonate activator as described above. The molybdate component (e.g. K2MoO4) and the peroxide component (e.g. H2O2) are dissolved within the microemulsion to form the desired peroxomolybdate compounds. The hydrogen peroxide is generally added in batches to the medium. It generates 1O2,but also some water as a side product derived both from the disproportionation and from the water of dilution of hydrogen peroxide.
The microemulsion should ideally be designed to meet three requirements: no phase separation during storage and during the oxidation reaction, high solubility of the reactants (e.g. peroxide and molybdate components), and simple recovery of the oxidized product, surfactant, and catalyst (molybdate compound) at the end of the reaction. Furthermore, none of the components of the microemulsion itself should react with the peroxide, molybdate or the intermediates derived therefrom (peroxomolybdates and singlet oxygen). In an alternate embodiment, the peroxomolybdate compound may be dispersed in a water-surfactant medium. The water-surfactant medium may include any of the surfactants described above, and may further include one or more co-solvents from the list described above.
In the preferred embodiment of the invention, the microemulsion exhibits stability at a temperature of from about xe2x88x9230xc2x0 C. to about xe2x88x9240xc2x0 C., more preferably from about xe2x88x9240xc2x0 C. to about xe2x88x9245xc2x0 C., and most preferably from about xe2x88x9245xc2x0 C. to about xe2x88x9250xc2x0 C. Additionally, the microemulsion is preferably maintained at a pH of from about 7 to about 12, more preferably from about 7.5 to about 11, and most preferably from about 8 to about 10.
Once the peroxomolybdate compound is formed and blended with a suitable medium, the compound is contacted with at least one chemical warfare agent having a formula described above. The contact may be accomplished by immersing a chemical warfare agent covered article into a solution containing the described peroxomolybdate species, spraying the peroxomolybdate compound onto an article, or other means for reacting the peroxomolybdate with the chemical warfare agent. The agent is contacted with the peroxomolybdate compound for a time and under conditions sufficient to oxidize the agent into a non-toxic oxide. For example, when the blister agent mustard gas (HD), bis(2-chlorocthyl)sulfide, is contacted with a peroxomolybdate compound of the invention, it is oxidized to its corresponding sulfoxide according to the reaction below: 
wherein x=0-3. While this reaction occurs quite rapidly, some secondary oxidation to the corresponding sulfone does occur, but this reaction occurs at about two orders of magnitude slower than the initial reaction. The amounts, conditions and time required to achieve the desired result will, of course, vary somewhat based upon the type and amount of agent present and the area to be treated.